Brush containing polypropylene bristles



March 15,- 1966 'P. c. MUNT 3,239,865

BRUSH CONTAINING POLYPROPYLENE BRISTLES Filed March 24, 1965 2 Sheets-Sheet 1 INVENTOR PLUMMER 6. HUNT March 15, 1966 P. c. MUNT 3,239,8$5

BRUSH CONTAINING POLYPROPYLENE BRISTLES Filed March 24, 1965 2 Sheets-Sheet 2 m PL UMMER ga I BY M 3,239,865 BRUSH CONTAINING POLYPROPYLENE BRISTLES Plummer C. Munt, Burlington, Vt., assignor to E. B. & A. C. Whiting Company Filed Mar. 24, 1965, Ser. No. 442,322 2 Claims. (Cl. 15-159) This application is a continuation-in-part of application Serial No. 242,965, filed December 7, 1962, now abandoned, which was a continuation-in-part of application Serial No. 49,011, filed August 11, 1960, now abandoned.

This invention relates to oriented polypropylene filamentary bristles having a novel cross sectional configuration and to a brush containing such bristles. This invention also relates to a novel process for maintaining the dimensional stability of polypropylene filaments or bristles produced by melt spinning, cooling and subsequently drawing of heat softened filaments. More particularly, this invention relates to a process for producing bristles, having diameters of from about 8 to 120 mils and having a cross sectional shape the periphery of which is curvilinear, wi-thout materially distorting the transverse or cross sectional dimensions of such bristles during the production thereof.

It is well known that filaments or bristles of polypropylene may have their properties materially enhanced by drawing or stretching the filaments to increase the molecular orientation along the fiber axis. The resultant stretch oriented filaments are characterized by increased tensile strength, low elongation, and increased stiffness and resiliency. In stretch orienting heat softened filaments of polypropylene, the filament is often supported by some solid surface after it has been softened, but before it is stretched. For example, the filament may be passed through a heating zone wherein the filaments are heated to a temperature within their softening range by the action of a hot liquid or a hot gas in the heating zone. In order to expose the polypropylene filaments to the fluid source of heat for a period of time sufficient to raise the temperature thereof to a point within its softening range, the filaments are frequently conducted through a sinuous path within the heating zone by means of supporting rolls. Such rolls may themselves be independently heated so that they will serve as the source of heat for heating the filaments. In such a case, the fluid source of heat in the zone may be dispensed with. When polypropylene filaments :are passed directly through a heating zone unsupported by rolls or other surfaces While in the zone, there may be provided a device such as a roll assembly on the outside of the zone for snubbing the filaments after they have been heat softened but before they are stretched or drawn.

When a polypropylene filament having a circular cross section of suificient diameter to serve as a brush bristle (i.e., from about 8 to 120 mils) is cooled to solidify it subsequent to extrusion,the filament undergoes severe cross sectional distortion. Thus, when such an extruded polypropylene filament having a circular cross section is cooled to solidify it prior to softening it for stretch orientation, the filament does not retain its circular cross sectional shape but acquires instead an elliptical cross setcional shape. This phenomenon is known as out of roundness.

Moreover, the out of roundness is accentuated when such a filament, after being heat softened, is supported by a solid surface prior to and/or during the drawing thereof. The tension applied to the filament during the stretching operation causes the filament to press against the snub rolls. This factor increases the out of roundness.

The out of roundness, or cross sectional distortion, may

tilted States Patent e iC be so pronounced that the length of the major axis of the elliptical cross sectional shape of the distorted filament may be two or more times greater than the length of the minor axis thereof. This phenomenon may best be illustrated by reference to the relative dimensions of the cross sectional shape of the filament. The relative dimension of the cross sectional shape of a filament or dimensional ratio, is the ratio of the length of the major axis to the length of the minor axis. Thus, if the cross sectional shape of the filament is substantially circular, both axes are substantially the same length and the relative dimension of the cross section or dimensional ratio is substantially unity. However, when the length of the major axis is twice as great as the length of the minor axis, the relative dimension or dimensional ratio is 2.0.

The foregoing described disadvantages are avoided by the practice of this invention which, briefly, comprises pro viding an oriented polypropylene filament having a diam eter of from about 8 to 120 mils and having a lobate cross section which contains four peripheral lobes. Such a filament is produced by melt extruding a filament of polypropylene having a lobate cross sectional shape containing four peripheral lobes, quenching in a liquid bath or otherwise cooled to solidify the filament, subsequently softening the fiilament, and longitudinally stretching said filament. Prior to and/or during the stretching of the filament, it may be supported on a solid surface. The relative dimension or dimensional ratio of the filaments produced in accordance with this invention varies less than about five percent from that of the extruded filament. This provides exceptional stability both as to cross sectional shape and relative dimension not heretofore possible in prior processes.

In carrying out this invention, the filament has a cross section which contains four, preferably symmetrical, lobes. That is, the cross section is in the form of a quatrefoil. The peripheral lobes may be interconnected or the lobes may be spaced at intervals on the periphery of the cross section. It is preferred, as stated above, that the lobate elements of the cross section of the filament be symmetricali.e., that each of the lobes be of the same size and shape as the remaining lobes. The center of the cross section will then be equi-distant from the outermost points on the periphery of each lobe. The individual lobular elements forming the lobate structurei.e., the lobes per semay be circular or elliptical or pairs of opposing lobes may be lemniscate in shape. The size of the re-entrant angles or cusps which are formed at the point where one lobe converges with another lobs may vary widely. Therefore, this angle may range from about 20 degrees up to about 120 degrees. This angle is preferably about degrees.

The filament having a lobate cross section is preferably formed by melt extruding the polypropylene through an appropriately shaped extrusion orifice in a die such as are shown by US. Patents 1,773,696 to Dreyfus et al., dated August 26, 1930; 2,508,799 to Reis, dated May 23, 1950; and 2,746,839 to Terry et al., dated May 22, 1956. The disclosures of these patents relating to methods and apparatus for forming lobate filaments are hereby incorporated herein by reference; and particularly, the disclosures thereof relating to orifices for extruding lobate filaments.

The filament may also be formed in other ways such as by separately melt extruding three or more circular filaments and then uniting or jointing the filaments along their longitudinal axis such as by heating them until they become fused at their connecting surfaces. Such method is disclosed in U.S. Patent 2,149,425 to Draemann, dated April 5, 1935, the disclosure of which is also incorporated herein by reference.

After the filament having the lobate cross sectional shape is formed, it may be solidified as by quenching in a non-solvent bath or by air cooling. Subsequently, it is heat softened by some suitable means. This may be accomplished by conducting it through a heating chamber wherein it is supported, preferably, by a plurality of rolls or equivalent supporting members, the peripheral surface of each providing a supporting surface. The filament may be heated while in the heating zone by means of a fluid source of heat, either gas or liquid, or by means of independently heated rolls. Alternatively, the supporting rolls may be eliminated from the heating zone and the filament passed directly through the zone which is heated by some fluid source of heat, or by radiant heat, the filament being unsupported by any member providing a supporting surface which is located within the heating zone. In such a case, the softened filament may be snubbed by means of a suitable device such as a conventional snubbing roll assembly after it leaves the heating chamber but prior to the drawing operation. Thus, the heat softened filament may be supported by the surface of the snubbing device after it leaves the heating zone and is in a softened condition.

After the filament has been softened, it is stretched longitudinally to increase the molecular orientation along the fiber axis. Any amount of stretching will increase the molecular orientation. However, maximum benefits are attained by stretching the filaments from about 6 to about 11 or more times of their length.

The cross-sectional shape of the drawn filament prepared according to this invention is substantially the same as that of the undrawn filament after it is extruded but before it is solidified and subsequently heat softened prior to the drawing thereof. That is, the relative distance between the midpoint of the cross section and the points on the periphery, or the relative dimensions, remain approximately or nearly the same so that, although the size or area of the cross section are considerably less after drawing, the configuration remains substantially the same.

The preferred polypropylene which may be used in the practice of this invention is isotactic polypropylene which is a high molecular weight (i.e., above about 45,000) solid polymer exhibiting a crystalline X-ray diffraction pattern. Such a polymer has a density between 0.90 and 0.94 and a melting point above about 320 F. These polymers may be prepared by methods now well known in the art such as the procedures described by G. Natta in the Journal of Polymer Science, vol. XVI, pp 143 to 154 (1955) and in US. Patents 2,882,263; 2,874,153; and 2,913,442.

The aspects of this invention which are capable of illustration are shown in the accompanying drawings.

FIGURE 1 is a schematic view of a suitable overall arrangement of apparatus for carrying out the method of this invention.

FIGURE 2 is a schematic view of a section of a modification of the apparatus shown in FIGURE 1.

FIGURE 3 shows the cross sectional shape of filaments produced by the process of this invention.

FIGURE 4 is a schematic view of another apparatus suitable for carrying out this invention in which the filament is softened in a heating chamber which does not contain any supporting surface in the heating chamber itself.

FIGURE 5 shows a brush containing lobate polypropylene bristles.

In FIGURE 1, a hopper contains pellets 11 of the polypropylene starting material such as crystalline isotactic polypropylene. The pellets 11 may be preheated in the hopper 10 if desired. From the hopper 10 the pellets are conveyed by means of a heated screw mechanism 12 to a heated extrusion head 13 which contains an extrusion die 130. In the extrusion head 13, the temperature of the material is raised to above its melting point. It is extruded through suitably shaped orifices in the extrusion die 13a into one or more filaments 14. A preferred extrusion temperature for the isotactic polypropylene is about 480 F. when the filaments 14 are extruded at a linear rate of from about 18 to about 30 feet per minute from the orifices, the size of which may range up to about 500 mils in diameter. The extrusion orifices are shaped so that the extruded filament will have a quatrefoil shape as shown in FIGURE 3. In FIGURE 3, the re-entrant angles 22 are formed at the points where the lobes converge on the periphery of the cross section.

In drawing extruded filaments of isotactic polypropylene, it is advantageous to quench the extruded filaments in order to solidify them. Quenching at a temperature below about 60 F. imparts valuable properties to the drawn polypropylene as described in applicants Patent 3,059,991 (the disclosure of which is incorporated herein by reference). This may be accomplished, as shown in FIGURE 1, by placing a quench bath 15 between the extrusion head 13 and the heating chamber 22. The extruded filaments 14 are guided into the quench bath 15, containing a liquid non-solvent for isotactic polypropylene, e.g., water, by a guide roll 16. The bath 15 is maintained in a suitable tank 17 at a temperature of 60 F. or below. Temperatures of about 40 F. are preferred. An immersion time of from about 8 seconds to about 20 seconds of the filaments 14 in the bath 15 is generally sufficient. The filaments 14 are transported around a stationary pin 18 in the quench bath 15 and then over the roll 19 and into the hot air conditioning oven 22. In the oven, the extruded filaments are transported over a number of rolls 20, which may be heated, in a sinuous or zigzag path, as heated air is circulated from overhead as indicated by the arrows. As the filaments pass through the heating zone, each succeeding driven roll 20 over which the filaments 14 pass is driven at a slightly increased peripheral speed from that of the preceding roll so as to prevent the filaments from sagging appreciably. The primary purpose of the series of driven rolls 20 is to provide a heat exchange relationship between the filaments 14 and the heated air in the oven whereby the filaments are uniformly softened by heat. Since isotactic polypropylene has a softening temperature in the range of from about 260 F. to about 305 F., it is preferred to maintain the temperature in the oven at about 300 F.

After leaving the last and uppermost driven roll 20, the filaments are snubbed with a three roll assembly 21, each roll of which is driven at about the same as or a higher peripheral speed than that of the last driven roll 20. A fast snub roll assembly 23 is provided just outside the oven 22 which is driven at a peripheral speed of about 6 to 11 times that of the assembly rolls 21. Thereby, the filaments 14 are stretched from about 6 to 11 times their length. This increases the molecular orientation along the fiber axis. The drawn, oriented filaments 14 are thereafter collected on a reel 24 which is supported on a frame 25.

FIGURE 2 illustrates a modification of the apparatus shown in FIGURE 1 in which extruded filaments 14 are solidified by air cooling rather than by quenching. The filaments 14 are passed over the rolls 31 to allow them to solidify prior to being transported into the hot air conditioning oven 22.

In FIGURE 4, filaments 40 having lobate cross sectional shapes prepared by means, previously described, are passed over a snub roll assembly 39 and thence into the heating chamber 41. A fluid heating means, such as super heated steam, is circulated through the heating chamber. The fluid is introduced into the heating chamber through the inlet 42 and removed through the outlet 43. The temperature of the heating chamber is maintained at a temperature sufficient to soften the filaments. The heat softened filaments are snubbed by the roll assembly 44 immediately after they leave the heating chamber. These rolls are driven at a slightly higher peripheral speed than the rate at which the filaments are passed into the heating chamber so as to keep the filaments from sagging appreciably while in the chamber. After being snubbed by the roll assembly 44 the softened filaments are drawn to several times of their length by a fast roll 45 which is driven at a peripheral speed of about 6 to 11 or more times than that of the snub roll assembly 44. The filaments may then be collected on a conventional reel assembly such as described in FIG- URE 1.

FIGURE 5 illustrates a conventional brush 50 which comprises a handle 51 containing brush bristles 52 of oriented melt extruded isotactic polypropylene. The brush bristles 52 have lobate cross sections containing 4 peripheral lobes. The bristles have diameters of from 8 to lZO-mils.

The following examples illustrate the best mode contemplated for carrying out this invention:

EXAMPLE 1 Isotactic polypropylene having an average molecular weight of about 100,000, a density of 0.90 and a crystalline melting point of 333 F. was fed into a screw extruder of the type shown in FIGURE 1 having a 3.5 inch screw diameter. The die plate contained 9 extrusion orifices, each having the shape of a four leaf clover. The jacket was heated to a temperature of about 480 F. and the filaments were extruded at a linear rate of about 25 feet per minute from the orifices. The cross section of each of the extruded filaments contained four symmetrical, converging lobes such as shown in FIGURE 3. The horizontal axis of the cross section measured 130 mils and the vertical axis measured 125 mils. The ratio of the length of the horizontal axis to that of the vertical axis was 1.04. The filaments were passed through a quench bath maintained at a temperature of about 40 C. to solidify them. They were then fed into a heating chamber and were transported over a series of rolls. Hot air was circulated through the heating chamber, thereby heating the filaments to a temperature of about 300 F. before they left the heating chamber. After leaving the heating chamber, the filaments were stretched to about ten times their original length. The cross sections of the drawn filaments were of the same shape as the cross sections of the filaments after they were extruded but before they were quenched and taken over the series of rolls in the heating chamber. The horizontal axis of the cross section of the drawn filament, was 43 mils in length and the vertical axis was 40 mils in length. The ratio of the length of the horizontal axis to the vertical axis was 1.075. Thus, as can be seen, the relative dimensions of the cross section varied by only about 3.4 percent.

By way of contrast, the process of the preceding example was duplicated wth the sole exception that the extrusion orifice was shaped so that the extruded filament had a substantially circular cross section before it was quenched. The horizontal axis was 130 mils in length and a vertical axis of the cross section was 125 mils. After the filament had been quenched and transported on rolls through the heating chamber and stretched to about ten times its original length, the cross section of the drawn filament was elliptical in shape rather than circular. The horizontal axis (major axis) was 50 mils and the vertical (minor) axis was 33 mils. The ratio of the length of the horizontal axis to that of the vertical axis before the filament entered the quench bath was 1.04. However, after they had been quenched, reheated and drawn, the ratio was 1.50, a distortion of about 44 percent or about thirteen times as great as that of Example 1.

lobes, eight lobes and round, were extruded and quenched as described in Example 1. The quench bath was maintained at a temperature of about 40 F. The filaments were then fed into a heating chamber where they were heated to a softening temperature of about 300 F. while being transported over rolls and were then stretched to about ten times their original length. These four filaments were all prepared sequentially during the same run and under the same conditions, except for the shape of the extruder die orifice. On each filament, the length of the vertical axis was about equal to the length of the horizontal axis after extrusion but before quenching and, therefore, the ratio of the length of the horizontal axis to that of the vertical axis was about unity. After they were quenched, heat softened and stretched, the vertical axis of the cross section of each filament was of the same approximate size of 40 mil +1 mil. The ratios of the length of the horizontal axis to that of the vertical axis of each fiber after it was heat softened and stretched are given in the following table.

Table Ratio of length of horizon- Cross-sectronal shape an axis to that of EXAMPLE 3 Using the modification of the apparatus shown in FIGURE 2, isotactic polypropylene filaments having cross sections containing four lobes were extruded by the process described in Example 1. The horizontal axis of the cross section of each filament measured 37 mils and the vertical axis measured 35 mils. The ratio of the length of the horizontal axis to that of the vertical axis was 1.05. The filaments were subsequently passed over a series of rolls to allow them to solidify at room temperature. They were then fed into a heating chamber where they were heated to a softening temperature. After leaving the heating chamber, the filaments were stretched to about ten times their original length. The horizontal axis of the cross section of the drawn filaments was 12 mils and the vertical axis was 11 mils. The ratio of the length of the horizontal axis to the vertical axis was 1.09.

Uniformly shaped filaments produced by the process of this invention are extremely useful in the production of uniform tufts of high bulking bristles in a brush. This results in a more uniform distribution of wear of the bristles. Moreover, such tufts are more easily mounted in brush heads. In addition, the rib-like ridges extending longitudinally along the surface of each filament provide added strength. In tufts composed of such bristles there is an interlocking between adjacent bristles which prevents relative movement therebetween during fiexure in use. Furthermore, flex action in any direction is much more nearly uniform than in oval filamentsi.e., filaments which have gone out of round during processing. Also, the tetralobate filamentary bristles of this invention possess good stiffness. The lobes at the end of the filament tend to split and separate in use in a brush resulting in a brush with a soft, flagged tip. This renders the brush more efficient in sweeping of fine sand and dust than a brush made of a solid filament of large diameter. Because of the stiffness of the major portion of each bristle, the brush or broom containing these bristles is still capable of picking up heavy debris and large objects. By applying the proper amount of heat and pressure to the center of the tetralobal bristles, it is relatively easy to collapse the tetralobal structure to give a flattened portion of the bristles, thereby rendering them easier to bend in this area and facilitating the cable filling of street brooms.

I claim:

1. A brush containing brush bristles of draw-oriented melt extruded, isotactic polypropylene having a density between 0.90 and 0.94, said bristles having lobate cross sections containing four peripheral lobes and having diameters of at least about 8 mils, said bristles having been stretched from about 6 to 11 times their original length, the change in the relative dimensional ratio of the cross sectional shape of said bristles being varied by less than about 5% from the relative dimensional ratio of the cross sectional shape of said bristles before draw-orientation, the cross section of said bristles having major and minor axes perpendicular to each other passing through the center of said cross section, the ratio of the length of the major axis to the length of the minor axis being not greater than about 1.09.

2. A brush bristle of draw-oriented, melt extruded, isotactic polypropylene having a density between 0.90 and 0.94, said bristle having a lobate cross section containing four peripheral lobes and having a diameter of at least about 8 mils, said bristle having been stretched from about 6 to 11 times its original length, the change in the relative dimensional ratio of the cross sectional shape of said bristle being varied by less than about 5% from the relative dimensional ratio of the cross sectional shape of said bristle before draw-orientation, the cross section of said bristle having major and minor axes perpendicular to each other passing through the center of said cross section, the ratio of the length of the major axis to the length of the minor axis being not greater than about 1.09.

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCES Review of Textile Progress: The Textile Institute, C. Tinling & Co., Ltd., December 1957, vol. 8, pages 85 and 86. (Copy available in Scientific Library.)

CHARLES A. WILLMUTH, Primary Examiner. 

2. A BRUSH BRISTLE OF DRAW-OREINTED MELT EXTRUDED, ISOTACTIC POLYPROPYLENE HAVING A DENSITY BETWEEN 0.90 AND 0.94 SAID BRISTLE HAVING A LOBATE CROSS SECTION CONTAINING FOUR PERIPHERAL LOBES AND HAVING A DIAMETER OF AT LEAST ABOUT 8 MILS, SAID BRISTLE HAVING BEEN STRETCHED FROM ABOUT 6 TO 11 TIMES ITS ORIGINAL LENGTH, THE CHANGE IN THE RELATIVE DIMENSIONAL RATIO OF THE CROSS SECTIONAL SHAPE OF SAID BRISTLE BEING VARIED BY LESS THAN ABOUT 5% FROM THE RELATIVE DIMENSIONAL RATION OF THE CROSS SECTIONAL 